Nutrition is vital to health and the availability of resources has long been acknowledged as a key factor in the ability to fight off parasites, as investing in the immune system is costly. Resources have typically been considered as something of a “black box”, with the quantity of available food being used as a proxy for resource limitation. However, food is a complex mixture of macro- and micronutrients, the precise balance of which determines an animal's fitness. Here we use a state-space modelling approach, the Geometric Framework for Nutrition (GFN), to assess for the first time, how the balance and amount of nutrients affects an animal's ability to mount an immune response to a pathogenic infection. Spodoptera littoralis caterpillars were assigned to one of 20 diets that varied in the ratio of macronutrients (protein and carbohydrate) and their calorie content to cover a large region of nutrient space. Caterpillars were then handled or injected with either live or dead Xenorhabdus nematophila bacterial cells. The expression of nine genes (5 immune, 4 non-immune) was measured 20 h post immune challenge. For two of the immune genes (PPO and Lysozyme) we also measured the relevant functional immune response in the hemolymph. Gene expression and functional immune responses were then mapped against nutritional intake. The expression of all immune genes was up-regulated by injection with dead bacteria, but only those in the IMD pathway (Moricin and Relish) were substantially up-regulated by both dead and live bacterial challenge. Functional immune responses increased with the protein content of the diet but the expression of immune genes was much less predictable. Our results indicate that diet does play an important role in the ability of an animal to mount an adequate immune response, with the availability of protein being the most important predictor of the functional (physiological) immune response. Importantly, however, immune gene expression responds quite differently to functional immunity and we would caution against using gene expression as a proxy for immune investment, as it is unlikely to be reliable indicator of the immune response, except under specific dietary conditions.

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Grazing by large herbivorous mammals is still a structuring force in tropical grassy ecosystems, and cattle grazing is one of the main economic activities carried out in these ecosystems in modern times. Therefore, understanding the impacts of cattle grazing removal on biodiversity may be a key step for conservation of this ecosystem. Here, we studied the successional trajectory of dung beetle communities in a tropical grassy ecosystem after cattle removal. For this, we assessed the patterns of dung beetle taxonomic and functional diversity of 14 natural grasslands with distinct cattle grazing removal ages (from 3 months to 22 years) along a chronosequence, applying the space-for-time substitution method. Our results show a strong decrease in dung beetle abundance (93 times) and species richness (6 times) in the first ten years of cattle removal. However, after ten years there is an increase in dung beetle abundance (73 times) and species richness (5 times). Taxonomic composition was also influenced by cattle removal time demonstrating the importance of cattle in the structuring of dung beetle communities in natural grasslands. In contrast, functional composition and diversity were not affected by cattle grazing removal, indicating these metrics are less sensitive to cattle absence than taxonomic diversity and composition. Our results provide evidence that cattle grazing removal, at least in the short term (10 years), may be an inefficient management tool for restoration and conservation of tropical grassy ecosystems. However, we highlight the need to investigate the reintroduction of cattle grazing after different removal times to provide complimentary information to livestock management able to integrate human use and conservation of tropical grassy ecosystems.

Cotton plants produce gossypol as a major secondary metabolite to resist insect herbivores and pathogens. Helicoverpa armigera may employ multigene families of detoxification enzymes to deal with this metabolite. So far, the strength of the transcriptional response to gossypol detoxification in the cotton bollworms remains poorly understood. Here, we investigated the genomewide transcriptional changes that occur in cotton bollworm larvae after one generation feeding on various host plants (cotton, corn, soybean and chili) or an artificial diet. Six genes potentially involved in detoxification of xenobiotics were highly upregulated in bollworms fed on cotton, and the expression of five of these differed significantly in insects that fed on gossypol diet compared with the artificial diet. When these six genes were downregulated using RNA interference, downregulation only of CYP4L11, CYP6AB9 and CCE001b led to reduced growth of bollworm larvae feeding on gossypol diets. These data suggest that the three genes are involved in response of H. armigera to gossypol of cotton. Our results proved that H. armigera may have a broad mechanism for gossypol detoxification.

BackgroudHorizontal gene transfer and gene duplication are two major mechanisms contributing to the evolutionary adaptation of organisms. Previously, polygalacturonase genes (PGs) were independently horizontally transferred and underwent multiple duplications in insects (e.g., mirid bugs and beetles). Here, we chose three phytozoophagous mirid bugs (Adelphocoris suturalis, A. fasciaticollis, A. lineolatus) and one zoophytophagous mirid bug (Nesidiocoris tenuis) to detect whether the duplication, molecular evolution, and expression levels of PGs were related to host range expansion in mirid bugs.ResultsBy RNA-seq, we reported 30, 20, 19 and 8 PGs in A. suturalis, A. fasciaticollis, A. lineolatus and N. tenuis, respectively. Interestingly, the number of PGs was significantly positive correlation to the number of host plants (P = 0.0339) in mirid bugs. Most PGs (> 17) were highly expressed in the three phytozoophagous mirid bugs, while only one PG was relatively highly expressed in the zoophytophagous mirid bug. Natural selection analysis clearly showed that a significant relaxation of selection pressure acted on the PGs in zoophytophagous mirid bugs (K = 0.546, P = 0.0158) rather than in phytozoophagous mirid bugs (K = 1, P = 0.92), suggesting a function constraint of PGs in phytozoophagous mirid bugs.ConclusionTaken together with gene duplication, molecular evolution, and expression levels, our results suggest that PGs are more strictly required by phytozoophagous than by zoophytophagous mirid bugs and that the duplication of PGs is associated with the expansion of host plant ranges in mirid bugs.Electronic supplementary materialThe online version of this article (10.1186/s12862-019-1351-1) contains supplementary material, which is available to authorized users.